Abstract

The object of this thesis is the study and simulation of the connection of small wind turbines in battery based systems and the creation of a simulation that maximizes the energy production, based on the optimal cable cross-section and generator air gap.

As an introduction to the subject of the thesis, the benefits of renewable energy sources and small scale projects are presented. Then, the essential aerodynamic principles needed for modeling the wind blades, the turbine orientation and the calculation of the energy production are laid out. Furthermore, the thesis sets the theoretical background for the operation of the axial flow permanent magnet generators and the fundamental topologies are presented.

Next, the concept of microgrids is introduced and the models of AC and DC wind turbine connection analysis are explored. The thesis then describes how the modeling of a wind turbine in direct battery connection is done using the Simulink Matlab interface and the corresponding models are analyzed.

The thesis then presents the experimental measurements that ratify the electrical part of the wind turbine in direct battery connection and compares those to the results produced from the simulation modeling.

Going on, the thesis analyzes the international standard for measuring the power curve and then describes the small wind turbine test site in Rafina. After that, the thesis presents the measurements of the Furling angle used to find the equation that connects the Furling angle to the wind speed and the power curve and compares them to the results produced from the simulation modeling.

The process of determining the wind turbine specifications using the Method of Finite Elements is then presented, as well as the way to calculate the annual energy production.

The writer goes on to analyze the process of finding the optimal cable resistance for maximizing energy production, choose the optimal cable cross-section and carry out a cost analysis. Next, the process of finding the optimal air gap is explained and the results of the annual energy production depending on the distance of the wind turbine from the batteries are presented.

Lastly, the results of the direct connection of the wind turbine to batteries are compared with the results of the connection through MPPT, conclusions are deducted and further optimizations are proposed.

Key words: small wind turbine, low cost, axial flux generators, permanent magnets, microgrids, MPPT, direct battery connection, furling angle, maximizing energy production, optimal cable cross- section, optimal generator air gap

Author: Katerina Chira

Responsible PhD: Kostas Latoufis / latoufis@power.ece.ntua.gr

Supervising Professor: Nikos Hatziargyriou / nh@power.ece.ntua.gr

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